Method and device for controlling slip and/or for determining the longitudinal force or a flex work-proportional parameter, and vehicle tire therefore

ABSTRACT

A method for determining a longitudinal force acting during tire rotation on a tire mounted on a wheel rim includes the step of determining the torsional deformation of the tire, which is a function of the location of measurement, between a radially inner area of the wheel or the hub and a radially outer area of the tire in at least one non-rotating position. At least two marks are positioned at the wheel on different radii relative to an axis of rotation of the wheel, wherein a radially outer mark is positioned on a radially outer area of the tire. At least two sensors are non-rotatingly arranged in the vicinity of the wheel so as to be positioned on the different radii, wherein a radially inwardly arranged sensor is connected to a steering knuckle and a radially outwardly arranged sensor is connected to a transverse suspension arm of the wheel suspension. For the rotating wheel at least one time period between passing of the at least two marks at the at least two sensors is recorded. The torsional deformation is computed from the at least one time period. The longitudinal force is calculated from the torsional deformation. Other tire parameters such as tire air pressure, footprint length, tire spring travel, load/pressure ratio can also be calculated with variants of the disclosed method.

BACKGROUND OF THE INVENTION

The invention relates to a method for making possible greatest possibleaccelerations via frictional engagement and a method for determining thelongitudinal force acting on a tire or the tire spring travel or thefootprint length or the load/pressure ratio and a device for determiningthe longitudinal force acting on a tire or the tire spring travel or thefootprint length or the load/pressure ratio during rotation and avehicle tire that is suitable for cooperation with the aforementioneddevice and/or for the aforementioned method.

A vehicle wheel in the context of this application is to be understoodas a combination of all components which, with the exception of smallload-depending deformations, are torsion-proof connected to one anotherand are designed for rotation. A wheel thus includes especially thetire, the wheel rim with wheel flange and wheel rim bowl, the valve, thehub, possibly sealing and/or securing rings attached thereto, brakedisks, anti-lock magnet wheels and optionally drive shafts.

The invention is intended to increase the safety level of motor vehicleson wheels that are provided with tires, especially pneumatic tires,that, at least in the longitudinal directions, in general also in thetransverse direction (one exception is the famous Metro in Parisprovided with pneumatic tires), can transmit forces onto the road etc.only by frictional engagement. In most operational states the maximumpossible frictional engagement is not even used; however, wherever it isnecessary to react to unpredictable events, for example, a vehicle aheadthat has spun out of control or a child running onto the street, so asto prevent dangerous situations, the attainability of greataccelerations is required, especially with negative sign, i.e., greatbraking forces.

It is known that the value of greatest possible acceleration dependssubstantially on the coefficient of friction between the tires and thestreet. It is furthermore known, that this coefficient of friction isaffected by the paring of the material street/tire, mostlyasphalt/rubber mixture, the air pressure, the footprint length, and alsothe tire tread profile and the weather conditions. Furthermore, it isknown that the coefficient of friction is a function of slip. Slip is tobe understood as the difference between circumferential velocity of thetire minus steering knuckle velocity, divided by the steering knucklevelocity.

FIG. 1 shows for the conventional frictional material pairing fortypical boundary conditions a curve of the coefficient of frictionμ_(longitudinal) as a function of slip, in the following referred to asslip curve. The maximum longitudinal coefficient of friction is reachedat a slip of approximately 10%. When the slip is increased further,which could be achieved during braking by increasing the braking moment,the coefficient of friction, together with the effective longitudinalforce, would not increase further but, to the contrary, would decrease.This not only would result in the problem that the braking decelerationwould decrease instantly, but would also lead to, when maintaining thetoo high braking moment, the wheel rotation frequency and thus thecircumferential velocity of the tire would be reduced quickly to zero(the quicker, the smaller the moment of inertia of the tire--and it isrelatively small in comparison to the vehicle mass). The operationalstate in which the wheel no longer rotates despite still presentsteering knuckle velocity, is called "locking". The slip is then -100%.

FIG. 2 shows in a solid line the slip curve for the same tire on coldice (more unfavorable for warmer ice), and, as a comparison, in a thindashed line the slip curve of FIG. 1 is shown again. The value μ_(max)is not only substantially lower but also occurs at smaller slip.

The runaway rotational deceleration of the tire occurring during vehicledeceleration, already at slightly increased braking moment, enhances thedrawback of the initially only somewhat too great braking slip: Itincreases quickly from, for example, -14% to -100% in its value. Due tothis effect of surpassing the slip, to which the maximum coefficient offriction is related, the area past this slip is often designated bypersons skilled in the art as instable slip area. The slip area between0° and this value is designated as stable. The slip to which the maximumcoefficient of friction is related is called critical slip.

The same fact holds true for drive slip that is too great. Spinningdrive wheels also effect negatively the safety of the vehicle, eventhough usually not as badly as braked wheels that lock. Furthermore, inthe conventional non-locking differentials, the drive force does notbreak down, as during braking, for each wheel but for the axle becausethe greater portion of the drive output is transmitted to the slippingwheel. For non-locking interaxle differentials the drive force wouldeven break down almost completely.

In addition to the decrease of the transmittable longitudinal force, forbraking with locking as well as for slipping drive wheels, the vehiclesafety in such operational states is impeded by the loss, in the case oflocking brakes the complete loss of the ability to transmit lateralforces. The straight running stability is thus only supported by thetranslatory inertia mass and the moment of inertia mass about thevertical vehicle axis; steering maneuvers are impossible.

Because of the great importance of adjusting the correct slip for therequirement of greatest possible positive or negative acceleration andbecause of the fact that a human being as a controller is usually onlycapable of simultaneously maintaining a maximum of two wheels within theoptimal slip range, as in the case of a motorcycle, whereby for allother motor vehicles including airplanes, in general, only one actuatingdevice for the entire number of wheel brakes is present, the developmentof slip control systems, i.e., of systems where a technical device takesover the control function performed by the human being began in theforties of this century, initially only for the braking systems ofairplane landing gear. When using such systems, the human being byadjusting the lever pressure, lever travel or pedal pressure or pedaltravel etc. only transmits his desire for controlling the nominal value,for example, the brake acceleration.

The control system, on the other hand, has been assigned the tank toadjust for each wheel individually the favorable slip. Most of the slipcontrol systems will only function when at one wheel almost the criticalslip has been reached. By preventing a further increase of the brake,respectively, drive moment, locking, respectively, slipping isprevented. Once the critical slip has been surpassed, for example, whenthe wheel suddenly encounters a worse frictional pairing as for exampleblue basalt etc., the control system reduces the brake, respectively,drive moment to such an extent and for such a period time until the sliphas been adjusted to just below the critical slip.

Slip control devices have been used for approximately 8 years in themass production of passenger cars, trucks and trailers with increasingmarket share. Insofar as they control only the brake slip, the acronymABS (derived from Anti Blocking System) has been used. Slip controlsystems prove their effectiveness especially impressively under suchdriving conditions where one wheel track runs on a surface with badmaximum coefficient of friction while the other wheel track runs on asurface with high maximum coefficient of friction.

Slip control systems according to the prior art detect very preciselythe actual rpm of each wheel. For this purpose, each wheel is providedwith a so-called magnet wheel that on a circumferential line comprises aplurality of marks, the passing of which is detected by a non-rotatinglyarranged sensor based on fluctuations of the magnetic flux. From thetime interval between passing of two adjacently arranged marks of themagnet wheel, the microcomputer of the control device calculates thewheel rpm and, after multiplication with a stored circumferentiallength, the circumferential velocity of the tire.

Based on this data the electronic control device calculates furthermorethe change of rpm or the circumferential velocity over time.

For detecting the actual slip, each slip control system requiresinformation in regard to the steering knuckle velocity. Since in mostoperational states of interest the velocity differences between thesteering knuckle (curve-inner steering knuckles somewhat slower thancurve-outer steering knuckles) are minimal, the slip control systemsknown to the inventors therefore set all steering knuckle velocities tobe equal to the (translatory) vehicle velocity. However, there remainsthe problem how to determine exactly this vehicle velocity.

For this purpose, the control device also determines, based on the rpmor circumferential velocities of a plurality of wheels at the vehicle,in general, of all wheels, the maximum (during braking), respectively,the minimum (during positive acceleration). Even though out of all wheelrotation information these extreme velocities, respectively, extreme rpmin reality correlate best with the vehicle velocity, but, it must stillbe considered fictitious as long as it is not measured slip-free, i.e.,free of braking and drive moments. Based on this possibly fictitiousvehicle velocity, the control device calculates the slip individuallyfor each wheel based on the wheel rotation information of the individualwheels.

When a vehicle over a longer period of time is braked with slip at allfour wheels, the possible deviation between the actual vehicle velocityand the aforementioned fictitiously calculated one increases steadily sothat the information basis is more and more dubious. When, however, thevehicle velocity can no longer be determined reliably, the system losesthe required information for reliable operation in regard to theindividual wheel slip, and the quality of the control decreases. Thisproblem exists for drive slip control systems as well as for brake slipcontrol systems when all axles are driven.

These problems can be overcome when in sufficiently short time intervalsat least one wheel is made substantially free of moments, and thecircumferential velocity of this wheel thus approaches the vehiclevelocity (intermittent braking). The time interval of making the wheelmoment-free can be shorter when the moment of inertia of the respectivewheel is minimal; however, the moments of inertia of wheels in thepassenger vehicle field have not been returned due to wider wheels andrims, stronger brakes, and stronger drive joints despite an increasinguse of light metal for the wheel rings. Unavoidably, when freeing thewheel of moments, the braking and acceleration capability is wasted.

In addition to the aforementioned comparison of the rotationalvelocities, it is also known for detecting over-critical slip at a wheeladditionally or alternatively, to use the comparison of the rotationalaccelerations. When at one wheel the value of rotational accelerationsurpasses the value of rotational acceleration at the other wheels, thisis interpreted as the beginning of locking, respectively, slipping andthe braking, respectively, drive moment of this wheel is controlled to asmaller value.

But even with this measuring method problems result when, for example,during the sudden occurrence of an oil stain, all wheels encounter arotational acceleration that is too great for the instant coefficient offriction. When the rotational accelerations have not yet increased to avalue that should not even be reached for μ=1, even an additionalprogram loop with a plausibility control does not help.

It is furthermore known that for some roadway coatings such as ice, snowor gravel up to this time no sufficient slip control has been possible.The slip curves for these conditions deviate greatly from the slip curvefor rubber/asphalt represented in FIG. 1. For a more exact understandingof the instantly applicable slip curve the control process could beimproved. This would entail the recognition of the roadway coating andan adaptation of the control behavior of the slip control device to theroadway coating.

In summary and abstraction, a problem of the known slip control systemis that it employs data for controlling the slip which have beenthemselves measured under slip conditions. It is a first object of theinvention to at least reduce the dependency on slip-dependently measuredvalues, respectively, to preferably overcome it.

Most vehicles driven by frictional engagement use tires which obtaintheir supporting capacity and their optimal frictional engagement valuesonly by filling with compressed air. When the tire pressure drops belowa threshold value depending on the wheel load, the safety is negativelyaffected by this also. Therefore, many systems for controlling the airpressure have been suggested. They all have the problem that the valueto be measured, i.e., the air pressure, is present within the rotatingwheel, but the measured value is to be used in a non-rotating system,for example, to be displayed at the dashboard.

Accordingly, all air pressure controlling devices can be divided intotwo main groups:

In a first group all suggestions are to be arranged where the interiorof the tire opens via a channel, penetrating the wheel rim and the hub,with a sliding sealing into the non-rotating steering knuckle and fromthere opens via a hose etc. into a non-rotating pressure meter. Suchsystems allow, in addition to the actual measuring, also the correctionof a possibly recognized error. A non-rotatingly arranged compressor isable to supply compressed air into the interior of the tire in thereverse direction. The disadvantage of all systems of this group is thelimited service life of the pressurized sliding seals and the relativelygreat leakage flow which not only allows for a compressor but almostmakes it necessary to have one for most applications. However, thisresults in additional weight, increased energy consumption, and aconsiderably higher purchase price.

In the second group all such suggestions are arranged where the pressuremeter is arranged in the rotating wheel and the measured data aresupplied to a non-rotating computing unit. This data transmission can beperformed with slip rings or by radio transmission. In any case, theexpenditure for such an arrangement is great. Slip rings increase thefrictional resistance and are subject to wear reducing the service life,radio transmitters require an energy supply into the rotating wheel oran energy source within the rotating wheel, for example, a battery.

It is thus a second object of the invention to monitor the presence ofsufficient air pressure in a simple and reliable manner.

SUMMARY OF THE INVENTION

The first object is solved in that the longitudinal force acting on thetire is determined and input into the control system. The suggestednovel detection of the longitudinal force allows the determination ofthe actual position on a slip curve not only, as known previously, basedon the abscissa, i.e. based on the actual slip value with allaforediscussed problems in regard to the required determination of thevehicle velocity, but based on the ordinate. The measured longitudinalforce of the tire divided by the wheel load results in the currentfrictional coefficient μ, i.e., the ordinate of the slip curve.

The precision with which the ordinate, i.e., currently used μ, can bedetermined, depends not only on the precision of measuring of thelongitudinal force, but also on the precision of the determination ofthe wheel load. Accordingly, the wheel load of each wheel is preferablymeasured also. This is universally possible with a piezo crystal ringbetween the steering knuckle and the inner bearing ring which mustdetect the deformation in the vertical direction of the vehicle. Onaxles without transverse suspension arms it is especially easy todetermine the wheel load at the spring element, for example, byexpansion measuring strips at the predominately used steel coil andtorsion spring arrangements, and for air springs by measuring therespective air pressure. Measuring at the spring element is alsopossible for axles with transverse suspension arms when additionallyalso its wheel load component is measured and added at one side andsubtracted on the other side of the same axle.

The newly suggested measuring of the longitudinal force can also becarried out with an optionally additional piezo crystal ring between thesteering knuckle and the inner bearing ring which, however, would haveto determine the deformation in the horizontal direction of the vehicle.

Furthermore, a wheel-individual longitudinal force measurement ispossible by measuring the bearing reaction forces at the connectinglocations of the longitudinal swinging arm or by attaching expansionmeasuring strips to the longitudinal swinging arms. On axles withtriangular transverse suspension arms, the measurement of the tworeaction forces occurring substantially in the axial direction of thevehicle, for example, is possible, preferably with a piezo crystal ringat least between a bolt at the car body and a corresponding eye, i.e.,the outer bearing ring of the transverse suspension arm. Multiplied bythe axial length of the triangular transverse suspension arm and dividedby the distance in the longitudinal direction of the vehicle between thetwo suspension locations of the triangular transverse suspension arm atthe car body, the longitudinal force results also, at least in theespecially important case of wheel turning angles of substantially zero.

In short, a longitudinal force measurement as well as a wheel loadmeasurement are possible very exactly and reliably over an extendedperiod of time because all required measured values can be taken atparts that will perform only finite pivoting movements but do not rotateendlessly, i.e., they do not rotate. The longitudinal force measurementallows, preferably combined with a wheel load measurement, an exactdetermination of the coefficient of friction μ currently used.

One could object to the suggested position determination on the slipcurve because only the function of μ over the slip is definedunequivocally while the inverse function, slip over μ, in most ranges ofthe values is ambiguous, i.e., most values of μ have correlated theretoan undercritical and an overcritical slip, however, such an objectioncarries no weight for a plurality of reasons:

Firstly, the known slip control systems also operate reliable only aslong as at least one wheel is within the undercritical range, and inthis range the inverse function is also defined underunambiguously.

Secondly, from the sum of all wheel loads the total vehicle mass can bededuced easily, and the actual vehicle acceleration results veryprecisely from the sum of all measured longitudinal forces divided bythe total vehicle mass. Based on this, the slip-free correspondingrotational acceleration for all wheels is determined. This informationopens a plurality of possibilities, especially:

a) The new method is combined with the known methods and allows, evenfor extended braking actions or all wheel accelerations, an improvedplausibility control of the actual wheel rotation accelerations.

b) While maintaining the conventional rotational velocity determinationand the deduced rotational acceleration computation, the braking anddrive moment is controlled such that the measured wheel rotationacceleration coincides at least in approximation with that determinedbased on the vehicle acceleration.

Thirdly, an oscillation overlap of the initially selected brake linepressure selected by the driver is to be recommended which, apart fromthe critical point of the slip curve, must appear in a periodicfluctuation of each wheel longitudinal force. In the stable range, alsocalled undercritical range, a brake line pressure increase results in adeterminable trailing longitudinal force increase that is of a shortduration and, while in the instable area, also called overcritical area,the reverse relation results, or, for certain street coatings, there isno correlation to be observed. The amplitude of the brake line pressurefluctuation can be selected to be astonishingly small in relation to thebrake line pressure which corresponds to the maximal suitable brakemoment, preferably 3% to 6%. The thus effected brake line loss issubstantially smaller than in previously known systems usingintermittent braking.

In combination with the known slip control systems it is furthermorepossible by data comparison of both measuring methods to quickly adaptautomatically the applied slip curve to the actual conditions: Forexample, when a conventional slip control system adjusts a slip of 9%,in expectation of reaching μ of approximately 0.85, and when thelongitudinal force measurement detects for example a μ of only 0.3, thenit is obvious that another slip curve must be used. It is possible tostore in the evaluation unit a plurality of slip curves and toautomatically select, when such a situation occurs, the best suitedcurve for each wheel. However, in combination with the previously knownslip control systems it is also possible via the wheel rpm measurementto update continuously the applied slip curve with a directedmeasurement of characteristic value pairs of the slip and μ, for eachwheel individually.

Summarizing the above description, the suggested longitudinal forcemeasurement allows, preferably in combination with a wheel loadmeasurement, in combination or alternative to the previously known wheelrpm measurement, a secure control behavior for extreme drivingconditions that are especially safety-relevant.

The inventors have furthermore recognized that the longitudinal forcecannot only be determined at the interface of the wheel suspension butalso from the deformation of the respective tire. This appears to beespecially attractive because especially a pneumatic tire can be viewedas a spring element so that the resulting deformations are greater thanat the elements of the wheel suspension. Thus, in principle, anexcellent measuring precision is possible.

Based on this--new--recognition, the inventors have thus selected as afurther object to provide a method which measures the actinglongitudinal force as directly as possible at the tire.

The measuring location tire appears to be attractive insofar as thecurrent coefficient of friction μ can be detected free of braking forceswhich allows for an especially fast control. However, the faster thecontrol (and the greater the movement of inertia of the wheel), the morecontrollable the instable slip range, and it becomes possible that theaverage over time of the slip achieved by the control coincides with thecritical slip and must not as previously maintain a "safety distance"which results in a longer braking distance on an ideal street withslip-controlled systems than without.

The present invention further to determine the longitudinal force actingon the tire as a result of the torsional deformation of the tire, thatdepends on the position of a plane containing the measuring elements andextending perpendicular to the rotational axis, between a radial innerarea of the wheel and a radial outer area of the wheel belonging to thistire in at least one non-rotating position. According to the presentinvention the thus determined longitudinal force is to be used in aslip-control method for allowing greatest possible positive and/ornegative accelerations of the vehicle.

However, the measuring location tire in the past was not an optionbecause, in contrast to undercarriage parts, it rotates, so that thereis the problem of transmitting the data error-free, reliably over anextended operation period, and inexpensively into a non-rotatingevaluation, display, and optionally intervention unit. As explained inthe following, "during the tire rotation" the detection of a certaindeformation type can be performed without encountering this problem.

When the local torsional deformation is measured only at a singlelocation, which is sufficient for longitudinal force determination, thenthis should be the position above the rotation axis in the verticaldirection of the vehicle. This location in the following is designatedas 0°. For the local torsional deformation in the context of thisapplication the term tire deformation is also used.

For explaining the measuring principle it should first be assumed,greatly simplified, that the normal force required for the frictionalforce build-up not only occurs within the closely defined footprint,which would be corresponding to the facts, but also over the entiretread surface. Then, the tread surface would have no need to deform to anon-round surface or to adopt at any location an eccentric shape.However, a rotation between the tire tread surface and the tire beadwould still occur. (To be precise, a rotation between the wheel rimflange and the hub would also occur, however, this rotation issubstantially smaller due to the substantially greater stiffness of themetals.) This effect is especially noticeable for the currentlypredominant construction of pneumatic tires, i.e., with atorsion-favoring radial carcass and a pulling and pressure resistantpackage of belt plies.

The rotational angle increases exactingly monotonously as a function ofthe torque causing the rotation. This relation is surprisingly close toa linear function.

According to the second object the sufficient level of air pressure isto be controlled, preferably as an additional measure. The inventorshave realized that for this purpose the measurement of the air pressureis unnecessarily complicated and provides unnecessarily weakinformation:

A somewhat lower air pressure than suggested in the owner's manual fornormal load conditions can be without consequence for extremely lowloads. On the other hand, even the normal air pressure can be too lowfor extremely high loading with the result of great tire flex work andthus too great tire heating and polymer degradation resulting therefrom.A control only of the air pressure would leave unconsidered thedependence of the required air pressure from the wheel load.

The inventors have recognized that for monitoring the safe operation ofa pneumatic wheel the flex work per revolution should be determined. Itis almost proportional to the spring travel of the tire as well as tothe footprint length and also to the ratio of the received wheel load tothe tire air pressure, in the following referred to as load/pressureratio.

For solving the second object they suggest according to claim 6 todetermine a parameter that is approximately proportional to the flexwork per revolution in that this parameter, i.e., the spring travel ofthe tire or the footprint length or the load/pressure ratio, isdetermined based on the position-dependent torsional deformation of thetire between a radially inner area and a radially outer area of the tirein at least two (of course, separate) not-rotating positions.Preferably, positions of approximately 180° are avoided. Especiallypreferred are position pairs of 0° and 90°, 90° and 270° as well as 270°and 0°. Here, the data processing is especially simple, as will beexplained in the following:

Coming from the thought experiment longitudinal force transmissionwithout wheel load, as explained above, now the discussion revert tothe--realistic--normal force introduction within the footprint alone:

It is clear that a rotation between the radially outer and radiallyinner area of the tire due to a braking or drive torque must occur,however, overlapped with deformations based on the non-uniformlydistributed wheel load action. For simplifying the explanation now asecond attempt: Wheel load introduction without longitudinal force (thiscase is even realistic, especially for braking-free and drive-freerolling):

The wheel load action at the tire tread surface not only results in atread surface flattening within the footprint but also, especially inconjunction with belt layers combined so as to be pulling and pressurestiff, in a tread surface deformation within the remaining periphery ofthe tire: Aside from small areas of the footprint leading edge andtrailing edge and, of course, of the footprint itself, the remainingtread surface area maintains substantially its circular shape, butsubstantially displaced eccentrically to the rotational axis in theupward direction by a small amount that is proportional to the wheelload. This deformation amount appears in the 0° position as a pure"pull", i.e., as a deformation to a greater radius from the rotationalaxis, in the 180° position as a pure pressure, and in the position 90°and 270° as a displacement in the circumferential direction which, as aphenomenon, is not to be discerned from the local torsion. However,while torsion resulting from torque without wheel load will appearuniformly over the entire circumference with respect to amount andorientation, the torsion due to wheel load without torque will besimilar to a sign oscillation. In the 0° position (pull) it is 0(therefore, when measuring in only one position, deducing from here theacting torque, respectively, the longitudinal force), in the 90°position depending on the sign definition it is a positive or negativemaximum, in the 180° position (pressure) it is again 0 (however, here isa risk of damage by curbs etc.), in the 270° position it is the maximumof same amount as in the 90° position but with reverse sign.

Especially preferred is the position combination 90° and 270° becausethe flex work proportional value is then the difference between the twomeasured values (which corresponds to an addition of two approximatelyidentical values because one of the two values has a negative sign) andbecause of the especially great total signal in comparison to theunavoidable measuring errors.

The different parameters, wheel load on the one hand and flexwork-proportional parameter on the other hand, effect easily discernablelocal torsion deformations in different positions. They fulfill verywell the rules of a linear superposition. In the last discussed 90°/270°position combination, for example, the longitudinal force results fromthe sum of the two measured values, the flex work-proportional parameterfrom the difference.

With the exception of the combination 0°/180° any other positioncombination is possible for the determination of the longitudinal forceas well as for the flex work-proportional parameter by programming theabove-described sign-shaped angular relations into the evaluation unit.Preferably, a method with torsional measurement in two positions servesnot only for the determination of one of the two parameters longitudinalforce and flex work-proportional value but for both.

When in even more positions measurements are performed, the thusresulting redundance can be used for determining the desired parameterswith different means. This results not only in a lowering of the failureprobability but also allows--as long as not too many sensors will failso that no redundance is present anymore--an averaging of the resultsdetermined in different ways in regard to the same parameter, so thatthe precision of the final results can be further increased.Furthermore, upon surpassing of a pre-selected difference between theresults measured in different ways for the same parameter, a warningdisplay of a functional failure at the dashboard is suitable.

The above explanations show that the measurement of the local tiretorsion is suitable for determining the longitudinal force as well asfor monitoring the respective required air pressure. It appears to beespecially elegant that such a measuring method can take care of bothtasks at the same time.

The value of the torsional deformation can be determined, for example,by measuring the transverse strain in a surface extending in thecircumferential direction. However, the respective sensors are difficultto place. Furthermore, it is complicated to transmit the relatively weakmeasured signals from the expansion measuring strip from the rotatingwheel to a non-rotating evaluation and display or intervention unit.

The inventors therefore see a further object in that the torsionaldeformation is to be described with such physical parameters which withminimal expenditure can be measured sufficiently precisely and which canbe transmitted easily and reliably into a non-rotating unit.

This object has also been solved, in particular with a furtherdevelopment of the previously disclosed method, especially in that thetorsional deformation is determined based on one or a plurality of timeperiod measurements whereby the time period(s) to be measured betweenpassing of at least two marks positioned at different radii to therotational axis at the rotating wheel, whereby at least the radiallyouter mark is positioned at a radially outer area of the tire, across atleast two non-rotating sensors positioned on the corresponding radius tothe rotational axis.

A device suitable therefore is taught in the present invention.

The radially inner sensor or sensors can be arranged for radiallyinwardly, even--and this is even attractive--on the cylinder mantlesurface or a collar (the projecting opposite to a groove) of thesteering knuckle. The cooperating mark(s) must then be positioned in orat the hub, for example, integrated into the sealing ring.

Of course, the radially inner mark(s) can also be positioned furtherradially outwardly, for example, in the vicinity of the wheel flangepositioned inwardly relative to the vehicle as long as a sufficientradial distance to the radially outwardly positioned mark(s) remainsbecause the measuring signals are greater when the radial distance,through which a respective radial extends, the phase position of whichrelative to one another is inventively determined. It is essential thatthe sensor or sensors are positioned on the same radius of therotational axis as the cooperating mark(s).

For some wheel suspensions it is recommended for reasons of simplicityto arrange the outer sensor(s) at the transverse suspension arm(s) ofthe wheel suspension.

The measuring principle is based on the radially outwardly arrangedmark(s) passing with a delay of a time difference delta t for positiveacceleration, the cooperating sensor(s) in comparison to the point(s) intime of passing of the radially further inwardly arranged mark(s) acrosstheir respective sensor(s). For a negative acceleration, i.e., forbraking, the outer mark(s) pass the corresponding sensor(s)correspondingly earlier or, expressed in reverse, the inner mark(s) passat a later time.

For a more detailed explanation in conjunction with FIGS. 3a through 3da simple case is discussed as an example, in which a pair of sensors 4and 5, shown only as a small square, are rigidly arranged in the 0°position, i.e., in the vertical radial line with respect to the vehicleabove the rotational axis, and two cooperating marks 2 and 3, indicatedby a small circle, on corresponding different radii R2 and R3 at therotating wheel.

The two marks in this example are not positioned on a common radial line(when considering the extension in the axial direction, this is morecorrectly called also "phase plane"). In contrast, they are displacedrelative to one another by the differential angle D which in the shownembodiment is 30°=pi/6. For a constant rpm n=1/T, whereby T is theperiod time, i.e., the time for one revolution of the wheel, the timespan between passing of the leading mark 2 at the sensor 4, which isshown in FIG. 3b, and passing of the mark 3 at the sensor 5, which isshown in FIG. 3c, is in general

    t.sub.2,3 =T×D/2pi, i.e., in this case T/12.

When, for example, caused by a negative acceleration, i.e., an actingbrake moment, the inner mark 2 is displaced to the rear by an angleAlpha about the axis of rotation RA relative to the orientation ofrotation, this results in an extension of the time span t₂,3 by theamount

    delta t.sub.2,3 =T×Alpha/2pi=Alpha/(2 pi n).

Thus, the fluctuation of the result of the time span measurementcorrelates in this example with the local torsion angle Alpha.

When, which is most important for the measuring of the parameterrelating to the flex work, it is also taken into consideration that thelocal torsional angle Alpha changes somewhat across the shown 30°interval, it must be said that the fluctuation of the time span t₂,3does not correlate with the torsion angle Alpha itself but with itsaverage value in a linear fashion in the position, here 15°, between thebeginning and the end of the time span measurement. When it is desiredto have an optimal correlation to the torsional deformation in the 0°position, it would be advantageous, for an otherwise unchanged example,to slant the common phase plane of the two sensors by 15°. The pilotproduction devices tested so far only need a mark difference angle of 3°(However, the actual conditions could not have been properly shown) sothat even without consideration of these minor details the resultingmeasuring results reflect reality extremely precisely.

As stated already in the above explanations, the torsion angle Alphacorrelates, in turn, as a function of the selected non-rotatingmeasuring locations, with the longitudinal force to be measured,respectively, the parameter based on the flex work. Thus, it is shownthat and in which manner the time span measurement is suitable fordetermining one or both desired parameters. Also, the required devicesare disclosed to such an extent that the average person skilled in theart is able to construct devices suitable for performing the method,especially because time measuring circuits are known in the prior art,also from the conventional slip measuring systems.

The decisive difference to the latter is that the inventive device notonly comprises radially inwardly positioned marks with a correspondingsensor, but also comprises at least one radially outer mark wherebybetween the radially outer mark(s) and the radially inner mark(s) acomponent of significant torsional softness is arranged, preferably atleast a part of a tire sidewall.

In comparison to conventional systems the advantage lies in a higherreliability even under difficult conditions. In contrast to a devicemeasuring the deformation travel or the deformation tension in therotating wheel, the advantage is that the measured data from thebeginning are sensed non-rotatingly, so that there is no need for anyerror-susceptible and/or expensive data transmission from a rotating toa non-rotating sub system. In this regard there is a similarity to theconventional slip control systems.

A further advantage of this method is that time span measurements, incomparison to tension measurements, angular measurements or lengthmeasurements, have an especially advantageous relation betweenprecision, long service life, and reliability, on the one hand, andpurchasing costs, on the other hand.

As an explanation of the operation the aforementioned equation

    delta t.sub.2,3 =T×Alpha/2pi=Alpha/(2 pi n)

is solved for Alpha. It reads then:

    Alpha=(2pi/T)×delta t.sub.2,3

or

    Alpha=2 pi n×delta t.sub.2,3.

In order to define the longitudinal force and the flex work-dependingparameter, when this is to be done very precisely, calibrating functionsmust be stored and used in the evaluating unit which calibratingfunctions are exactingly monotonous. First attempts, however, have shownthat already with a simple proportional factor, corresponding to alinear calibrating function, an astoundingly high measuring precisioncan be achieved. When it is desired to determine even more preciselythe, in general, slightly progressive, calibrating function and use it,then this is a routine measure known to the person skilled in the art.

In summarizing the above explanations, it is important that

a) in a radially outer area of the tire belonging to the wheel the pointin time (points in time) of passing of one or more marks arranged at thetire across the at least one outer non-rotating sensor must beregistered, in the following called the outer point or points in time,and

b) in a radially farther inner area of the wheel, the point in time(points in time) of passing of one or more marks positioned at thewheel, for example, within the tire bead area or at the rim or,preferably at the hub, passing across at least one inner non-rotatingsensor must be registered, in the following called the inner point orpoints in time, and,

c) the time period or time periods between the outer point or points intime and the inner point or points in time must be measured andevaluated

d) whereby the evaluation includes a division of the time period orperiods measured according to c) by the period length T to be determinedalso, whereby the period length corresponds to the time period for arevolution of the wheel or a certain fraction thereof.

It is possible that passing of an inner mark across an inner sensortriggers a respective time period measurement, preferably with anelectronic timer, and that passing of an outer mark across an outersensor stops this time period measurement. However, the opposite ispossible in that the passing of an outer mark across an outer sensorinitiates a time period measurement, preferably with an electronictimer, and the passing of an inner mark across an inner sensor stops thetime period measurement.

That one of the passing actions should stop the time period measurementthat has the smaller probability of error because then the probabilityof erroneous time period measurements is minimized. In such an errorscenario there would not be provided an erroneous but instead nomeasurement signal. This allows a simple error recognition and avoidsfalse results.

An arrangement of inner marks and sensors in the area of the hub,especially in the well-protected hub itself, appears to lead accordingto past experiences to an extremely minimal error probability. Thus, insuch an arrangement, the stopping function should be provided inwardly.However, when the inner marks and the sensors are arranged in the areaof the wheel rim flange, their function appears to provide a greatererror probability (for example, rim flange damage by fast travelingacross curbs) then the cooperation of the outer mark and sensors.Accordingly, the first described functional distribution is to berecommended.

As mentioned before, the differential angle between a pair of marks inthis application is indicated with "D". In the example according toFIGS. 3, D was 30°. However, a different differential angle between thephase plane of the sensors of a sensor pair is possible. This isindicated in this application with "d". This angle d was set to be 0° inFIGS. 3 for simplifying the explanation. However, since for achievingfavorable costs for the inventive device the required sensors would beplaced onto parts of the wheel suspension that are already present, sucha sensor pair differential angle would most likely not be 0. Theequation given on page 21 at the end of the second paragraph

    t.sub.2,3 =T×D/2pi

is to be generalized for d not 0 such that

    t.sub.2,3 =T×(D-d)/2pi.

It has been explained that the measuring precision is especially highwhen D as well as d are close to 0, in the extreme case are equal to 0.In this case, as in any other case with D-d equal 0 the time period t₂,3to be measured is equal to 0 for a scenario free of moments. When it ispreset that the outer mark 2 triggers the time period measurement andthe inner stops it, then at a position of 0° of the sensor pair, in thecase of braking, a time period t₂,3 equal delta t₂,3 almost proportionalto the value of the brake moment and thus to the value of thelongitudinal force is measured, for a maximum load approximately 1°.

For the case of positive acceleration, on the other hand, the completeperiod length T is provided. Because in the comparison to the muchlonger, approximately longer by the factor 360, period length, thedifference to T as an absolute value, which is of interest only, isalmost inconsequential, such a measuring result would thus be unsuitablefor controlling the drive slip. Furthermore, the lack of anorientational indication (+ or -) in this case, when no other provisionsare made, would not detect a driving longitudinal force but erroneouslyan exorbitantly high decelerating longitudinal force. Similar problemsare present when the torsional deformation for the determination of theflex work-depending parameter were to be determined at the rearwardwheel half, viewed in the driving direction, for example, in the 270°position.

The inventors have thus been faced with the further object of improvingthe aforementioned methods and devices such that the torsionaldeformations can be detected precisely in both orientations of rotationby time period measurements.

Two alternative solutions are provided for this.

The second solution is characterized in that the time period betweenpassing of the marks 2 and 3 as well as between passing of the marks 3and 2 are measured and of the two measured time periods one is providedwith a positive and the other with a negative sign, and of both timeperiods the one of a smaller absolute value will be used. When appliedto the aforementioned example, in the previously problematic scenario atorsional deformation of -1° would be detected instead of a deformationof 359°.

The sign definition could also be reversed, it is only important thatthe orientational change of the parameter to be measured corresponds toan orientational change of the measuring result.

The advantage of this method improvement is that D-d may be set to 0,especially also D=0 and d=0. With this, the absolutely greatest possiblemeasuring precision is achieved. Furthermore, the sign-containingmeasuring result can be especially easily interpreted. However, themeasuring expenditure is in principle twice as high as in the secondsolution to be explained in the following.

The second solution uses the fact that even the maximum occurringtorsional angle values that are responsible for the detected time periodchanges and are within a range of 1°, are small in comparison to thecomplete angle. In summarizing briefly, a sufficiently great offset isadjusted by correspondingly placing the marks and sensors, for example,2°, so that under all circumstances the measured time period changes arefree of sign changes, in the aforementioned embodiment are between 1°and 3°; 1° could, for example, belong to the maximum brakinglongitudinal force, 1.5 to a conventional braking longitudinal force, 2°to freedom of longitudinal force, 2.5° to a conventional forward driveforce, and 3° to the maximum possible forward drive force.

In more detail: The differential angle (D) of a pair of marks, comprisedof an inner and an outer mark, is defined as the angle between the phaseplane of one mark and the phase plane of the other mark, whereby thephase plane of a mark is defined as the plane containing the axis of thewheel in which the respective mark is arranged on the wheel. Thedifferential angle (d) of a sensor pair, comprised of an inner and outersensor, is defined as the angle between the position plane of one sensorand the position plane of the other sensor, whereby the position planeof a sensor is defined as the plane containing the wheel axis in whichthe respective sensor is non-rotatingly arranged.

Based on this, the method improvement is characterized in that foravoiding time periods of different sign the differential angle (D) ofthe pair of marks deviates from the differential angle (d) of the pairof sensors at least by the rotational angle between the outer and innerarea under maximum wheel load so that of the designated pair of marksonly a certain mark, i.e., either the inner or the outer mark, triggersthe time period measurement and the other mark, i.e., the outer,respectively, the inner mark, stops the time period measurement.Preferably, one of the two differential angles (either D or d) is set tobe zero.

In principle, it is already sufficient to arrange a single pair of markson the wheel to be monitored. Insofar as the marks must be arrangedadditionally at the tire, respectively, at the wheel, this lower extremehas the advantage that the expenditure is minimal. However, theresolution over time is relatively bad. Thus, it is recommended to usesuch measurement only for wheels operated at extremely high rpm, forexample, the relatively small wheels of a landing gear of fighter planeswith take-off velocities of approximately 350 km/h.

A better resolution of the determined longitudinal force and/or the flexwork per revolution (i.e., tire spring travel or footprint length orload/pressure ratio) results with a method improvement, according towhich a plurality of pairs of marks are arranged on the wheel.Preferably, each sensor pair should then measure per wheel revolution aplurality of changing time periods between the passing of the two marksof each pair comprised of an inner and an outer mark.

In view of the fact that the angle distances of one load extreme to theother are approximately 2°, for a simple avoidance of a mixup (that themark of one pair is falsely interpreted as the mark of a neighboringpair) the number of pairs of marks should have 180 as an upper limit. Itis even more recommendable when for the purpose of greater safety withregard to mixups at both ends a safety distance of 0.5° is maintained,i.e. for each pair of marks a range of 3° is kept free. The especiallyrecommended upper limit for the number of mark pairs is thus 120.

The processing of this number of measured values is simplified when,each of the mark pairs has the same differential angle. (For thispurpose, it is possible, but not required, to distribute the marksuniformly about the respective circumference. For a non-uniformdistribution in one of the two sets of marks, the other set of marksmust have the same non-uniformness so that the phase relation withineach pair of marks is identical. Both are variants of the inventivedevice However, this is not a necessary requirement.

When, for example, for reducing costs or for increasing the reliability,a separate application of marks at the tire within the outer range is tobe avoided, which is to be recommended for mass production, it ispossible, according to a further embodiment of the teaching, that anumber of wire ends of a belt ply could be extended in, preferablyuniform, circumferential distances at least on the tire side I whichwith respect to the vehicle faces axially inwardly, and that theseprojecting wire ends could be reliably detected with sensors, whichrespond to a change of the magnetic flux density.

In a non-uniform distribution of the mark pairs, this would result inthe advantage that for each measured value exactly the correspondingrotational position of the wheel could be detected. This would allow forthe additional detection of out-of-round or imbalance of the wheel.Furthermore, this allows for considerable simplifications in the designof the devices suitable for the method:

Most vehicle tires have transverse grooves in the tread strip profiling.The edge portion of the tread strip profiling, which is often called"side decoration" and during normal driving conditions is not in contactwith the road surface but is subjected to surface contact only upon aslanted approach on curbs, has often, for improving the curb climbingability, also transverse grooves, i.e., grooves not extending in thecircumferential direction, which are arranged, primarily for reasons ofstylistic consequences and the desired wide appearance of the tire, inalignment with the transverse grooves of the main area of the treadstrip which under normal driving conditions is in contact with the roadsurface. Accordingly, the transverse grooves of the side decoration arenot provided in uniform division, but according to the pitch sequence ofthe tread strip main area provided for reasons of noise reduction.

Especially in cooperation with sensors for the outer marks, that detectoptical signals, for example, respond to a change of light reflection ofthe object observed, the transverse grooves of the side decoration couldbe used as outer marks (2). Thus, no additional, not even a changed,component would be required at the tire.

Such an approach would also be possible, of course, when somewherewithin the tread surface main area and not within the side decoration, adetectable, preferably optically, transverse groove sequence would bepresent. However, the tire-near attachment of the outer sensor orsensors, due to the greater length of the connecting part between thesteering knuckle and the sensor, in the following called "outer sensorcarrier", would be more complicated. Furthermore, the sensor carrierwould be heavier and thus more prone to oscillation.

When it is desired to proceed such that despite the non-uniformdistribution of the mark pairs within each one of the mark pairs thedifferential angle is identical, both mark tracks (also called marksets) must be fine-tuned relative to one another such that the innermark track has exactly the same non-uniformness as the outer mark track.Since there is a great number of different pitch sequences, even withinthe tire types for a certain vehicle, in such a case it is recommendableto mount not only the outer mark track but also the inner mark track atthe tire, the latter preferably within the bead area, because in thisway complicated communication between the tire and the vehicle producerfor the purpose of matching can be avoided.

However, this would result in a more expensive tire. It is thus moreadvantageous to use also as inner marks such wheel parts that arealready present. In any conventional slip control system a magnet wheelwith a plurality of poles that are however uniformly distributed ispresent at each wheel. By abandoning a constant differential angle ofall mark pairs, it is possible to use as outer marks the (usuallynon-uniformly distributed) transverse grooves of the tire tread profile,especially of the side decoration, and to use as inner marks the(uniformly distributed) poles of an already present magnet wheel.

However, the processing unit must then be provided with more storage andcomputing capacity and must first determine the mark distribution forexample, with statistical computing programs or by comparison with dataof a conventional slip control system, must have the mark distributiontherein.

An extremely high number of mark pairs and the thus possible extremelyfine resolution of measuring of the longitudinal force and/or of theflex work-depending parameter thus possible over the rolling distance ofthe vehicle results, in view of the unavoidable sluggishness in thebrake and/or drive moment adjustment, only at low velocities or verygreat wheel diameters in a precise slip control behavior. On the otherhand, velocities below 20 km/h are hardly of interest because thebraking distance at these velocities is very short anyhow, even withoutuse of slip control systems. Thus, there is no noticeable improvementwhen for passenger cars the number of mark pairs is increased to morethan 40 and for trucks is increased to more than 80. It is thuspreferable, in order to avoid excessive costs, to limit the number ofinner marks, which in most cases require separate application at thewheel, to these numbers. Especially when the inventive methods anddevices are used not alternatively but in addition to the conventionalslip control systems, which is especially favorable, the conventionallytooth-shaped poles of the conventional magnet wheel can be used as theinner marks. The conventional pole number is in the same range asmentioned above. The one of the inventors is 24 and 96.

The conventional number of detectable transverse tire grooves atpassenger cars is between 61 and 79. When it is assumed that a passengercar has a magnet wheel with 44 poles and the mounted tire has 67transverse grooves, it is still possible to use the transverse groovesof the tire as outer marks when the processing unit of the slip controlsystem has a selection program which selects the most suitable marks formark pair formation. This entails especially the elimination of outermarks, i.e., a reduction of the number of marks that is too great.However, there are also exceptions in which it is expedient to eliminatea small number of marks from the smaller set; for example, 25 outer and2 inner marks could be eliminated in the processing. Such exceptions aremore probable when the pole distribution on the magnet wheel is alsonon-uniform which, however, has not been realized in the past.

Truck tire profiles are, in general, more coarse. Typical transversegroove numbers are, despite the greater wheel diameter, in the rangebetween 35 and 60, in general, approximately 45. There are slip controlsystems for trucks with magnet wheels of greater pole number. In suchcases, in contrast to the above discussed case, inner marks are to beeliminated.

Any elimination, independent of whether it is an inner or outer mark, isexpediently carried out such that the mark pairs are formed so thatunder all load conditions time periods free of sign change are measured.

It has already been explained in detail in which non-rotating positionsor position combinations which local torsion or torsions as a functionof the target parameters longitudinal force and/or flex work-dependingparameter will occur and, in reverse, can be determined from the torsionangles.

Since the measured time period changes are exactly proportional to thetorsional angles, the aforedisclosed also is valid for the preferredmethod and device improvements with measurement of time period changes.In order to be able to determine both target parameters, a plurality ofsensor pairs are arranged non-rotatingly in the vicinity of the wheel indifferent position planes. Then, each mark pair passing these differentsensor pairs effects thereat a time period measurement beginning withthe passing of the leading mark of this pair to the passing of thetrailing mark of this pair. The position combination 90°/270° upon usingtwo sensor pairs is preferred because of the greater signal values inmeasuring the flex work-depending parameters and because of simpler andthus much faster as well as less cost intensive data processing withinthe processing unit. Furthermore, this position combination also allowsa precise and data-technological simple (only one addition is required)determination of the longitudinal force. According to another preferredembodiment both measuring possibilities should be used. Accordingly, theespecially preferred devices are characterized by an arrangement of allfour sensors on a sensor carrier attached to the steering knuckle on acommon horizontal line of the vehicle. The correlated FIGS. 6 and 7 showsuch an arrangement.

With especially minimal error probability and especially minimalexpenditure the longitudinal force can be determined with an arrangementof a single sensor pair in the 0° position, i.e., on a vertical line ofthe vehicle extending through the axis of rotation. An especially highprecision is achieved by arranging two sensors on a sensor carrier fixedto the steering knuckle and extending upwardly. Such a device is shownin FIG. 4.

Preferably, a further sensor (10) is fixedly connected, preferably inthe 90° or in the 270° position, to the steering knuckle that isresponsive to the outer marks and determines the axial distance betweenit and any mark passing it. This allows for a measurement of thetransverse force of the tire especially precisely when a furtherdistance measuring sensor is arranged in the 0° position. A transverseforce measurement is meaningful when an emergency braking action isperformed not on a straight course but in a curve.

On a straight course in such an emergency situation the maximum possiblefrictional value should be used for deceleration. However, as aconsequence, the ability to transmit transverse forces becomes verysmall. When the device, however, as preferred, is able to detect bytransverse force measurement at each wheel an increased need oftransverse force transmission ability, it can reduce the adjusted slip,however, taking into account a reduced longitudinal force transmission,to such an extent that this need is satisfied, i.e., the vehicle remainssteerable. Even though an increased braking ability in front of asuddenly appearing obstacle already increases the active vehicle safetysubstantially, an ensured evasive ability increases this safety evenfurther in most emergency situations. When the obstacle appears on astraight course, maintening full stirrability would mean accepting alonger braking distance. Of course, the transverse force could also bemeasured at a transverse suspension arm or at another component actingin the same manner, for example, a longitudinal extending leaf spring ofa truck.

For reducing the unsprung mass it is, in contrast to the device shown inFIG. 4, at least as long as no great wheel turning angles occur, alsopossible to connect the sensor carrier to the car body. Such a device isshown in FIG. 5.

When, as shown therein, both sensors are arranged on a sensor carriermounted at the car body, it is necessary, in order to avoid mixups, forexample, that the exterior sensor upon great spring travel does notdetect passing of an inner mark, that either one of the furtherrequirements that the radial distance between the sensor and betweenmark tracks is greater than the spring travel of the wheel suspension,or that the passing of the marks of one track is detected by a differentphysical effect than the passing of the mark of the other track, forexample, the outer mark could be optically detected and the inner markelectromagnetically detected must be fulfilled.

Furthermore, it would be possible to mount only the outer sensor at thecar body and to mount the inner sensor at the steering knuckle,preferably at the mantle surface of the steering knuckle and,accordingly, the marks of the inner track within the wheel hub. Thecooperating inner marks and the respective sensor thus contribute onlyminimally to the unsprung mass and mixups between the inner and outermarks, even when using the same detection effect, are prevented.

However, with an arrangement of only a single sensor pair in any desiredarrangement it is not possible to determine the flex work-dependentparameter value. For this purpose, at least two sensor pairs arerequired. Thus, a combination of two different measuring positions forsensor pairs is taught, in particular the aforementioned 0° position andat least one of the aforementioned positions 90° or 270°. All of thesepreferred position combinations as well as a combination of all threepreferred positions are the subject matter of the present invention.

One inventive method variant accepts that for the determination of theflex-work proportional parameter as well as the longitudinal force onlyhalf of the time period difference, as occurs in the 90°/270° positioncombination, is available and that the measuring precision is somewhatsmaller. It has the advantage that in a disturbance situation of thesensor pair in the 90° or 270° position the longitudinal forceespecially important for the slip control can still be determinedperfectly. Only the determination of the flex work-proportionalparameter is no longer possible. Thus, when one is limited to the use oftwo sensor pairs, the failure probability of the longitudinal forcedetermination with a position combination that includes the 0° positionis as small as possible. In the 90°/270° position combination, on theother hand, the failure of any one of the four sensors would not onlymake the determination of the flex work-proportional parameterimpossible but also of the longitudinal force.

An especially favorable combination of reliability and precision isachieved when the device comprises three sensor pairs, one in the 0°position, the other in the 90° position, and the last one in the 270°position. Such a device should operate such that under normal operatingconditions the value(s) as determined at the 90° position and at the270° position are used, especially displayed and/or used for the controlof the brake and forward drive moments, that as a control the values ofthe position combination 0°/90° and 0°/270° are also determined andcompared to the aforementioned ones. When a small threshold value issurpassed, an error indication should occur. Furthermore, the computingunit should be able to detect implausible data and should prevent theiruse in further processing. Such an advantageous device is able to handlethe failure of any of the sensors, when necessary.

The flex work-proportional parameter, independent of it being the wheelspring travel or footprint length or load/pressure ratio, should bedetermined and upon surpassing a respective limit value a warning signalof too high air pressure should be given to the driver and/or theallowable maximum velocity, optionally external temperature and/ortire-type dependent, should be lowered such that a tire failure causedby too great flex work load is prevented. Since the determination of theflex work-proportional parameter with the torsion deformationdeterminations by measuring the time period change of marks passingacross sensors is cost-favorable, reliable, and surprisingly precise,this solution of the second object allows for a considerable safety gainwith limited additional costs. The cost/benefit ratio is substantiallymore favorable than in known solutions such as air pressure measurementwithin the rotating wheel with detrimental data transmission problems.

As has been explained above, the flex work proportional parameter, forexample, the tire spring travel, is proportional to the ratio betweenthe wheel load and the air pressure. When one of the two parameters,wheel load or air pressure is determined separately, the other value canbe determined without further measurement by a simple calculation, i.e.,

    Wheel load=load/pressure ratio x air pressure

respectively

    air pressure wheel=load/load/pressure-ratio

with a calibrated proportionality factor.

The separate parameter air pressure is however not of a direct safetyinterest. However, it is in any case a good service indicator. For thisreason, especially because the wheel load can be determined at anon-rotating part, for example, the spring leg, of these two variantsthe latter one is preferred. The, preferably individual, wheel loaddetermination allows an especially exact determination of the currentlypresent μ in connection with an inventive longitudinal forcedetermination and thus also an especially fine tuning of the brake,respectively, drive moments.

When the tire pressure is measured in the known manner, then, uponsurpassing a limit for the determined wheel load according to theaforementioned equation, a warning in regard to, preferably, too highwheel load or too low air pressure should be given to the driver and/orthe allowable maximum velocity, optionally external temperature and/ortire-type dependent, should be lowered such that a tire failure becauseof too great flex work load is avoided and/or the starting of thevehicle is prevented per se. When in contrast the wheel load is measuredin a manner known per se, then, upon falling below a limit for the tireair pressure, determined according to the above equation, a warningshould be sent to the driver with regard to too low air pressure and/orthe possible maximum velocity, optionally external temperature and/ortire type dependent, should be lowered to such an extent that tirefailure because of too great flex work load is prevented.

An inventive device with time period measurement for detecting thetorsional deformation requires at each monitored wheel two tracks ofmarks that can be twisted relative to one another. The radially innerone can, but must not be, arranged at the tire. When it is arranged atthe tire, it should be arranged as far as possible radially inwardly.Each mark track must contain at least one, preferably a plurality ofmarks. Accordingly, the tire must contain at least the outer mark track,preferably in its radially outer area, so that the detected torsionaltravel based on the time span change is as large as possible and thusalso the time span change itself.

The arrangement of the inner marks in the radially inner area of thetire has logistic advantages. Especially it is thus simply and reliablyensured that the inner mark track has the same pitch sequence as theouter, which is especially beneficial when the side decoration isoptically sensed, because thus a constant mark differential angle isprovided. At least when the detection of passing is optical, the marksshould be detectable upon passing of the corresponding sensor by beingembodied as projections or depressions. This is also true when changesof sound propagation distances are used for detection.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be explained in the following in conjunction withsome Figures. It is shown in:

FIG. 1 a curve representing the coefficient of friction as a function ofslip ("clip curve");

FIG. 2 a representation of the slip curve on ice for the same pairing ofmaterials as in FIG. 1, showing in dashed lines as a comparison thecurve of FIG. 1;

FIGS. 3a-3d in a schematic representation cooperating marks and sensorsrelative to a wheel;

FIG. 4 a section of an inventive McPherson wheel suspension with sensorsfixedly connected to the steering knuckle in a 0° position;

FIG. 5 a section of an inventive McPherson wheel suspension with sensorsconnected fixedly to the car body in a 0° position;

FIGS. 6 & 7 a section of an inventive McPherson wheel suspension withsensors connected to the steering knuckle in the 90° and 270° positions;

FIGS. 8 & 8a a section of the inventive McPherson wheel suspension withat least one inner sensor arranged in the 0° position directly fixedlyconnected on the steering knuckle and an outer sensor according to FIG.5;

FIG. 9 an inventive tire with a side decoration the transverse groovesof which are used as outer marks; and

FIG. 10 an inventive tire with a belt edge at the inner side facing thevehicle with individual projecting wire ends that thus differ from thesurroundings and are detectable.

DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 4 shows a section of the inventive McPherson wheel suspension witha wheel 1, a spring 15, a piston 16, and a cylinder unit 17. The piston16 is pivotably connected with its upper end to the car body 30.

The steering knuckle 19 is connected with the inner end facing thevehicle to the cylinder unit 17. Here, a transverse suspension arm 18engages which is pivotably connected to the car body 30. The steeringknuckle 19 supports with a wheel bearing 21 a wheel hub 20. The wheelbearing 21 is comprised of an inner ring 22 and an outer ring 23 and issealed to the right and to the left with a respective sealing ring 24,25.

A wheel rim 8 is mounted to the wheel hub 20. It supports externally apneumatic tire 9. Furthermore, at the hub 20 a brake disk 26 is mounted.

A brake caliper 27 with brake pads 28, 29 engages about the brake disk26. It (27) is fixedly connected to the cylinder unit 17.

At the inner side I of the tire 9 an outer mark 2 and an inner mark 3are shown.

The sensor carrier 31 which is fixedly connected to the steering knuckleand to the brake caliper 26 comprises an outer sensor 4 and an innersensor 5.

When the outer mark 2 passes the outer sensor 4, which is connected witha wire 32 to the processing unit 14, a timing device is started, whichis preferably electronic and quartz-controlled. When the inner mark 3passes the inner sensor 5, which is connected with a wire 33 to theprocessing unit 14, the aforementioned timer is stopped and the timeperiod t 2,3 is measured.

A load cell 12 at the upper end of the piston 16 is connected with awire 34 to the processing unit 14 for determining the wheel load.

The results of the computing unit 14 are supplied via a wire 35 to thedisplay unit 36. It (36) is preferably arranged within the interior ofthe vehicle and is comprised of an air pressure display 37 and an ABScontrol light 38.

FIG. 5 shows a section of the inventive McPherson wheel suspension witha spring 15, a piston 16, and a cylinder unit 17.

The piston 16 is pivotably connected with its upper end to the car body30. The steering knuckle 19 is fixedly connected with its end facinginwardly relative to the vehicle with the cylinder unit 17. A suspensionarm 18 engages thereat which is pivotably connected to the car body 30.The steering knuckle 19 supports with a wheel bearing 21 a wheel hub 20.The wheel bearing 21 is comprised of an inner ring 22 and an outer ring23 and is sealed to the right and to the left with a respective sealingring 24, 25.

The wheel rim 8 is mounted on the wheel hub 20. It supports externally apneumatic tire 9. Furthermore, the hub 20 has mounted thereon a brakedisk 26.

A brake caliper 27 with brake pads 28, 29 engages about the brake disk26. It (27) is fixedly connected to the cylinder unit 17.

At the inner side I of the tire 9 an outer mark 2 and an inner mark 3are shown.

The sensor carrier 31 which is fixedly connected to the car bodycomprises an outer sensor 4 and an inner sensor 5. Their radial distanceis greater than the spring travel.

When the outer mark 2 passes the outer sensor 4, which is connected withwire 32 to the processing unit 14, a timer is started which ispreferably electronic and quartz-controlled. When the inner mark 3passes the inner sensor 5, which is connected with wire 33 to theprocessing unit 14, the aforementioned timer is stopped and the timeperiod t 2,3 is measured.

A load cell 12 at the upper end of the piston 16 is connected with wire34 to the processing unit 14 for determining the wheel load.

In analogy to the FIG. 4 the results of the computing unit 14 aresupplied via wire 35 to the display unit 36. It (36) is preferablyarranged within the interior of the vehicle and is comprised of an airpressure display 37 and an ABS control light 38.

FIG. 6 shows a section of an inventive McPherson wheel suspension with aspring 15, a piston 16, and a cylinder unit 17. The piston 16 ispivotably connected with its upper end to the car body 30.

The steering knuckle 19 is connected with its end facing inwardly withrespect to the vehicle fixedly to the cylinder unit 17. A transversesuspension arm 18 engages thereat which is pivotably connected to thecar body 30. The steering knuckle 19 supports with a wheel bearing 21 awheel hub 20. The wheel bearing 21 is comprised of an inner ring 22 andan outer ring 23 and is sealed to the right and to the left with asealing ring 24, 25.

At the wheel hub 20 a wheel flange 8 is mounted. It supports externallya pneumatic tire 9. Furthermore, at the hub 20 a brake disk 26 ismounted.

A brake caliper 27 with brake pads 28, 29 engages about the brake disk26. It (27) is fixedly connected with the cylinder unit 17.

At the inner side of the tire 9 an outer mark 2 and an inner mark 3 areshown.

The outer mark 2 describes a radius R2 and the inner mark 3 describesthe radius R3.

When the outer mark 2 passes the non-represented outer sensor 4, whichis connected with a wire 32 to the computing unit 14, a timer is startedwhich is preferably electronic and quartz-controlled. When the innermark 3 passes the non-represented inner sensor 5 which is connected witha wire 33 to the processing unit 14, the aforementioned timer is stoppedand the time period t 2,3 is measured.

With a wire 34 a load cell 12 at the upper end of the piston 16 isconnected to the processing unit 14 for determining the wheel load.

FIG. 7 shows a view of FIG. 6 from the left for showing the arrangementof the sensors 4a, 4b, 5a, 5b and 10.

It shows the spring 15 with piston 16 and cylinder unit 17 to which (17)the sensor carrier 31 is fixedly connected and thus, in turn, is alsofixedly connected to the steering knuckle.

The sensor carrier 31 supports two outer sensors 4a and 4b, two innersensors 5a and 5b, and a sensor 10 which serves for measuring the axialdistances.

About the center point of the steering knuckle 19 the inner radius R3,on which the sensor 5a and 5b are arranged, and the outer radius R2, onwhich the sensors 4a, 4b and 10, are arranged are provided.

The sensors 4a, 4b, 5a, 5b, and 10 are connected with a respective wire32a, 32b, 33a, 33b and 39 to the processing unit 14.

Load cell 12 at the upper end of the piston 16 is connected with wire 34to the processing unit 14 for determining the wheel load.

In analogy to the FIGS. 4 through 6 the results of the processing unit14 are supplied via wire 35 to the display unit 36.

It (36) is preferably arranged within the interior of the vehicle and iscomprised of an air pressure display 36 and an ABS control light 38.

FIG. 8 shows a section of an inventive McPherson wheel suspension with aspring 15, a piston 16, and a cylinder unit 17. The piston 16 ispivotably connected with its upper end to a car body 30.

The steering knuckle 19 is connected with its end facing inwardly withrespect to the vehicle fixedly to the cylinder unit 17. Here, atransverse suspension arm 18 is provided which is pivotably connected tothe car body 30. The steering knuckle 19 supports a wheel bearing 21with a wheel hub 20. The wheel bearing 21 is comprised of an inner ring22 and an outer ring 23 and is sealed to the right and to the left witha sealing ring 24, 25.

At the wheel hub 20 a wheel rim 8 is mounted. It supports externally apneumatic tire 9. Furthermore, on the hub 20 a brake disk 26 is mounted.

A brake caliper 27 with brake pads 28, 29 engages about the brake disk26. It (27) is fixedly connected to the cylinder unit 17.

At the inner side I of the tire 9 an outer mark 2 is shown. Preferably,as in all previous Figures, the tire comprises for better resolution aplurality of marks which, however, in the shown representation are notvisible.

Furthermore, an inner mark 3 is provided at the sealing ring 25. Ofcourse, a plurality thereof is preferably present, as in the otherembodiments. Furthermore, the number of inner marks preferably coincideswith the number of outer marks. The plurality of inner marks is shown inFIG. 8a which will be explained later.

The sensor carrier 31 which is fixedly connected to the car body 30comprises an outer sensor 4. The inner sensor 5 is fastened to thesteering knuckle 19.

When the outer mark 2 passes the outer sensor 4, which is connected viawire 32 to the processing unit 14, a timer which is preferablyelectronic and quartz-controlled is started. When the inner mark 3passes the inner sensor 5, which is connected via wire 33 to theprocessing unit 14, the aforementioned timer is stopped and the timeperiod t 2,3 is measured.

A load cell 12 at the upper end of the piston 16 is connected with wire34 to the processing unit 14 for determining the wheel load.

In analogy to FIGS. 4 through 7, the results of the processing unit 14are supplied via wire 35 to the display unit 36. It (36) is preferablyarranged in the interior of the vehicle and is comprised of an airpressure display 37 and an ABS control light 38.

FIG. 8a shows the sealing ring in a view from the inner side of thevehicle. The sealing ring contains a sheet metal ring with inner teeththe tooth-shape projections of which in the radially inward directionare used as inner marks 3. They are detected by an inner sensor or innersensors 5, in the shown embodiment only one directly connected to thesteering knuckle 19 so as to be rotationally fixed. The sheet metal ringwhich provides the marks is preferably, as shown in the embodiment,vulcanized to the sealing ring 25 so that it cannot be lost.

FIG. 9 shows the inventive tire 9 in a side view. The circular arc R2describes the position of the marks which are distributed at thedecoration.

FIG. 10 shows a perspective view of an inventive tire 9 with exposedbelt edges. The marks 2 are represented here as wire ends of the lowerbelt layer that project outwardly in a regular sequence. The projectingends should not project from the rubber, as shown here.

The present invention is, of course, in no way restricted to thespecific disclosure of the specification and drawings, but alsoencompasses any modifications within the scope of the appended claims.

We claim:
 1. A method for determining a longitudinal force acting duringtire rotation on a tire mounted on a wheel rim, said method comprisingthe steps of:A) determining the torsional deformation of the tire, whichis a function of the location of measurement, between a radially innerarea of the wheel or the hub and a radially outer area of the tire in atleast one position by the steps of:1) positioning at least two marks atthe wheel on different radii relative to an axis of rotation of thewheel, wherein a radially outer mark is positioned on a radially outerarea of the tire; 2) arranging at least two sensors non-rotatingly inthe vicinity of the wheel so as to be positioned on the different radii;3) recording for the rotating wheel at least one time period betweenpassing of the at least two marks at the at least two sensors; 4)computing the torsional deformation from the at least one time period;B) calculating the longitudinal force from the torsional deformation. 2.A method according to claim 1, further comprising the step ofdetermining the wheel load acting on the tire from the torsionaldeformation of the tire determined at least at two non-rotatingpositions.
 3. A method according to claim 1, wherein said step A) 3)includes detecting at the radially outer area of the tire at least onefirst point in time at which the at least one mark at the tire passesthe at least one outer non-rotating sensor; detecting at the radiallyinner area of the wheel at least one second point in time at which theat least one mark at the wheel passes the at least one innernon-rotating sensor; and measuring the time period between said firstand second points in time; said method further comprising the step ofprocessing the time period, wherein the time period is divided by aperiod length identical to an amount of time of one revolution of thewheel or a fraction thereof.
 4. A method according to claim 3, whereinthe step of detecting the first point in time triggers beginning of thestep of measuring the time period and wherein the step of detecting thesecond point in time triggers stopping of the step of measuring.
 5. Amethod according to claim 3, wherein the step of detecting the secondpoint in time triggers beginning of the step of measuring the timeperiod and wherein the step of detecting the first point in timetriggers stopping of the step of measuring.
 6. A method according toclaim 3, wherein:the step of detecting the first point in time triggersbeginning of the step of measuring a first one of the time periods andthe step of detecting the second point in time triggers stopping of thestep of measuring; the step of detecting the second point in timetriggers beginning of the step of measuring a second one of the timeperiods and wherein the step of detecting the first point in timetriggers stopping of the step of measuring; one of the first and secondtime periods is given a negative sign and the other is given a positivesign; in said step of processing that one of the first and second timeperiods is used that has a smaller absolute value.
 7. A method accordingto claim 3, wherein:the marks form a mark pair consisting of an innermark at the radially inner area and an outer mark at the radially outerarea, each mark positioned in a phase plane, defined as a planecontaining the axis of rotation of the wheel in which plane therespective mark is positioned, the inner and outer marks of the markpair having a differential angle relative to one another, thedifferential angle defined between the phase plane of the inner mark andthe phase plane of the outer mark; the sensors form a sensor pairconsisting of an inner sensor at the radially inner area and an outersensor at the radially outer area, each sensor positioned in a positionplane, defined as a plane containing the axis of rotation of the wheelin which plane the respective sensor is non-rotatingly positioned, theinner and outer sensors of the sensor pair having a differential anglerelative to one another, the differential angle defined between theposition plane of the inner sensor and the position plane of the outersensor; for preventing time periods of different signs, the differentialangle of the mark pair deviates from the differential angle of thesensor pair by at least the torsional angle between the outer and innerareas under maximum load of the wheel; one of the inner and outer marksof the mark pair triggers measuring of the time period and the other oneof the inner and outer marks of the mark pair stops measuring of thetime period.
 8. A method according to claim 7, wherein the differentialangle of the mark pair is zero.
 9. A method according to claim 7,wherein the differential angle of the sensor pair is zero.
 10. A methodaccording to claim 7, wherein a plurality of mark pairs are provided onthe wheel and wherein each sensor pair measures per revolution of thewheel all time periods between passing of the inner and outer marks ofeach mark pair.
 11. A method according to claim 7, wherein all markpairs have the same differential angle.
 12. A method according to claim7, wherein the mark pairs are distributed about the wheel circumferenceat different spacings to one another.
 13. A method according to claim 7,wherein a plurality of said sensor pairs are arranged non-rotatingly indifferent position planes in the vicinity of the wheel and wherein eachmark pair causes each sensor pair to measure the time period betweenpassing of the inner and outer marks.
 14. A method according to claim13, wherein a position vertical above the axis of rotation is defined as0° and wherein other positions are designated according to their anglein the wheel rotation direction relative to the 0° position, wherein twosensor pairs are provided, wherein a first sensor pair is positioned ata 90° or 270° position and a second sensor pair is positioned oppositelyat a 90° or 270° position, wherein the time periods measured in the twoopposite positions are added to one another and the resulting timeperiod sum is used to calculate, according to an empirically knownequation of tire longitudinal force as a function of the time period sumor the tire distortion angle in the 90° and 270° positions, the value ofthe tire longitudinal force.
 15. A method according to claim 14, whereinthe time periods measured in the two opposite positions are subtractedfrom one another and the resulting time period difference is used tocalculate, according to the empirically known equation of tire springtravel in the footprint or the footprint length as a function of thetime period difference or the tire distortion angle in the 90° and 270°positions, the value of at least one of the parameters tire springtravel or footprint length or load/pressure ratio.
 16. A methodaccording to claim 13, further including the steps of:measuring the tireair pressure with a rotating pressure meter at the wheel, said pressuremeter having a radio transmission unit for transmitting measured data toa non-rotating processing unit; determining the wheel load from themeasured air pressure and the load/pressure ratio.
 17. A methodaccording to claim 16, further comprising the steps of:upon surpassing awheel load limit, giving the driver a warning in regard to too greatwheel load of too little tire air pressure; and/or lowering the maximumdriving velocity, while taking into consideration exterior temperatureand/or tire type, to such an extent that tire failure due to too greatflex work load is prevented; and/or preventing starting of the vehicle.18. A method according to claim 13, further including the stepsof:measuring the wheel load with a known device at a suspension spring;determining the tire air pressure from wheel load and the load/pressureratio.
 19. A method according to claim 18, comprising the steps of:whenthe air pressure falls below a pressure limit, giving the driver awarning in regard to too low tire air pressure; and/or lowering themaximum driving velocity, while taking into consideration exteriortemperature and/or tire type, to such an extent that tire failure due totoo great flex work load is prevented.
 20. A method according to claim13, further including the step of storing the tire distortion as afunction of tire spring travel or a footprint length or a load/pressureratio and the tire longitudinal force, wherein the time periods measuredand divided by the period length is a value for the tire distortion. 21.A method according to claim 13, wherein the tire spring travel or afootprint length or a load/pressure ratio is determined, furtherincluding the steps of:comparing the tire spring travel or footprintlength or load/pressure ratio to a limit value; when the limit issurpassed, giving the driver a warning in regard to too low tire airpressure and/or lowering the maximum driving velocity, while taking intoconsideration exterior temperature and/or tire type, to such an extentthat tire failure due to too great flex work load is prevented.
 22. Amethod according to claim 3, wherein a position vertical above the axisof rotation is defined as 0° and wherein other positions are designatedaccording to their angle in the wheel rotation direction relative to the0° position, wherein said sensors are arranged in pairs and a firstsensor pair is arranged in the 0° and the time period measured in the 0°position, which is substantially independent of the tire spring traveland the footprint length, is used to calculate the value of the tirelongitudinal force according to the empirical equation of the tirelongitudinal force as a function of the time period or the tiredistortion angle in the 0° position.
 23. A method according to claim 22,wherein a second sensor pair is positioned in the 90° or the 270°position, wherein time periods measured by the first and second sensorpairs approximately simultaneously are processed by the followingsteps:calculating the current tire longitudinal force according to theempirical equation of the tire longitudinal force as a function of thetime period or the tire distortion angle from the time period measuredin the 0° position; subtracting the time period measured in the 90° or270° position from the time period measured in the 0° position anddetermining the absolute value of the resulting time period difference;calculating the value of tire spring travel or footprint length orload/pressure ratio from the resulting time period difference accordingto the empirically known equation of tire spring travel in the footprintor the footprint length or the load/pressure ratio as a function of thetime period or the tire distortion angle.
 24. A method according toclaim 1, wherein a position vertical above the axis of rotation isdefined as 0° and wherein other positions are designated according totheir angle in the wheel rotation direction relative to the 0° position,further including the step of:at the 0° position and at the 90° or 270°position providing a respective non-rotating sensor capable of measuringan axial distance between the sensor and the passing marks; determiningfrom the measured pairs of axial distances a transverse force acting onthe tire.
 25. A method according to claim 1, wherein in said step A) 2)a radially inwardly arranged sensor is connected to a steering knuckleand a radially outwardly arranged sensor is connected to a transversesuspension arm of the wheel suspension.
 26. A method for determining atire spring travel or a footprint length or a load/pressure ratio duringtire rotation, said method comprising the steps of:A) determining thetorsional deformation of the tire, which is a function of the locationof measurement, between a radially inner area of the wheel and aradially outer area of the tire in at least two positions, wherein atleast one of said two positions is not vertically above or below an axisof rotation of the wheel, by the steps of:1) positioning at least twomarks at the wheel on different radii relative to an axis of rotation ofthe wheel, wherein a radially outer mark is positioned on a radiallyouter area of the tire; 2) arranging at least two sensors non-rotatinglyin the vicinity of the wheel so as to be positioned on the differentradii; 3) measuring for the rotating wheel at least one time periodbetween passing of the at least two marks at the at least two sensors;4) computing the torsional deformation from the at least one timeperiod; B) calculating the tire spring travel or the footprint length orthe load/pressure ratio from the torsional deformation.
 27. A methodaccording to claim 26, wherein a position vertical above the axis ofrotation is defined as 0° and wherein other positions are designatedaccording to their angle in the wheel rotation direction relative to the0° position, wherein the sensors form sensor pairs, wherein a firstsensor pair is positioned at a 90° or 270° position and a second sensorpair is positioned oppositely at a 90° or 270° position, wherein thetime periods measured in the two opposite positions are subtracted fromone another and the resulting time period difference is used tocalculate, according to the empirically known equation of tire springtravel in the footprint or the footprint length as a function of thetime period difference or the tire distortion angle in the 90° and 270°positions, the value of tire spring travel or footprint length orload/pressure ratio.
 28. A method according to claim 26, wherein in saidstep A) 2) a radially inwardly arranged sensor is connected to asteering knuckle and a radially outwardly arranged sensor is connectedto a transverse suspension arm of the wheel suspension.
 29. A device fordetermining any of the tire parameters, acting during tire rotation on atire mounted on a wheel rim, selected from the group consisting of alongitudinal force, a tire spring travel, a footprint length, and aload/pressure ratio, said device comprising:at least one first markconnected to the tire on a radially outer area of the tire at a firstradius relative to the axis of rotation of the wheel; at least onesecond mark provided at the wheel in a radially inner area of the wheelat a second radius relative to the axis of rotation of the wheel; atleast one first sensor non-rotatingly arranged at the first radiusrelative to said axis of rotation for recognizing passing of said atleast one first mark; at least one second sensor non-rotatingly arrangedat the second radius relative to said axis of rotation for recognizingpassing of said at least one second mark; a measuring unit, operativelyconnected to said at least one first and second sensors, for measuringat least one time period between passing of said at least one first andsecond marks; a processing unit for determining from the at least onetime period any of said tire parameters.
 30. A device according to claim29, wherein said at least one second mark is connected to a wheelcomponent selected from the group consisting of a wheel rim flange and ahub.
 31. A device according to claim 29, wherein said at least onesecond mark is provided in the area of the tire bead.
 32. A deviceaccording to claim 29, wherein said processing unit comprises a circuitfor dividing the at least one time period by a corresponding measuredperiod length to determine thereby a local torsional angle between saidat least one first and second marks at locations determined by said atleast one first and second sensors, said processing unit furthercomprising a data storage unit in which the equations for said tireparameters as a function of said torsional angle are stored, whereinsaid processing unit calculates the desired one of said tire parametersbased on the determined torsional angles.
 33. A device according toclaim 29, wherein said at least one first mark is displaced relative tosaid at least one second mark in a circumferential direction of thetire.
 34. A device according to claim 29, wherein said at least onefirst sensor responds to magnetic flux density changes.
 35. A deviceaccording to claim 34, wherein the tire to be monitored has at least onebelt ply consisting of steel cords, said at least one belt ply having acut edge at a side of the tire facing inwardly relative to the vehicle,wherein at least one of the steel cords has a free end projectingaxially inwardly and functioning as said at least one first mark.
 36. Adevice according to claim 35, wherein every third steel cord has a freeend functioning as said at least one first mark.
 37. A device accordingto claim 29, wherein said at least one first sensor responds to a changeof light reflection, wherein the tire to be monitored has an inner tireside facing axially inwardly relative to the vehicle, wherein the innertire side has a tire tread profiling or shoulder profiling with at leastone transverse groove not extending in a circumferential direction ofthe tire, wherein said at least one transverse groove is said at leastone first mark.
 38. A device according to claim 29, having a fistoperational state in which, at a substantially constant vehiclevelocity, a phase position of said first marks relative to one anotheror relative to one another and said at least one second mark is detectedand stored in said processing unit.
 39. A device according to claim 29,having a first operational state in which, at a substantially constantvehicle velocity, a phase position of said at least one first markrelative to said at least one second mark is detected and stored in saidprocessing unit.
 40. A device according to claim 29, wherein a number ofsaid first marks differs from a number of said second marks, whereinsaid processing unit includes a selection program and wherein saidselection program, for forming mark pairs consisting of one of saidfirst marks and one of said second marks, selects the most suitable onesof said first and second marks for forming said mark pairs.
 41. A deviceaccording to claim 29, wherein said first marks and said second marksform mark pairs, consisting of one of said first marks and one of saidsecond marks, and wherein a differential angle between phase positionsof said first and second marks of each one of said mark pairs isidentical for all of said mark pairs or different wherein for differentdifferential angles said processing unit includes a statisticalevaluation program for measuring and storing the different differentialangles in order to correct the measured time period therewith.
 42. Adevice according to claim 41, wherein said mark pairs are distributed ina circumferential direction of the tire at different spacings to oneanother.
 43. A device according to claim 29, wherein said at least onefirst sensor and said at least one second sensor form sensor pairs,consisting of one of said first sensor and one of said second sensors,and wherein at least one of said sensor pairs is positioned in a 0°position defined as vertically above the wheel axiswherein, when two ofsaid sensor pairs are provided, a second one of said sensor pairs,relative to said sensor pair positioned in said 0° position, ispositioned in a 90° or a 270° position defined in the wheel rotationdirection; wherein, when three of said sensor pairs are provided, asecond and a third one of said sensor pairs, relative to said sensorpair positioned in said 0° position, are positioned in a 90° and a 270°position, respectively.
 44. A device according to claim 43, wherein aplurality of said sensor pairs is provided in a circumferentialdirection of the wheel.
 45. A device according to claim 29, wherein saidat least one first sensor and said at least one second sensor formsensor pairs, consisting of one of said first sensors and one of saidsecond sensors, and wherein one of said sensor pairs is positioned in90° position and a second one of said sensor pairs in a 270° position,relative to a 0° position defined as vertically above the wheel axis.46. A device according to claim 29 for determining the load/pressureratio, further comprising a tire air pressure measuring device whereinsaid processing unit is connected to said tire air pressure measuringdevice for calculating the tire air pressure.
 47. A device according toclaim 29 for determining the load/pressure ratio, further comprising awheel load measuring device wherein said processing unit is connected tosaid wheel load measuring device for calculating the wheel load.
 48. Adevice according to claim 29 for determining the load/pressure ratio,said device having means for generating a warning for the driver orlimiting the maximum velocity when a vehicle-specific limit of theload/pressure ratio is surpassed.
 49. A device according to claim 29 fordetermining the load/pressure ratio, said device having means forgenerating a warning for the driver and limiting the maximum velocitywhen a vehicle-specific limit of the load/pressure ratio is surpassed.50. A device according to claim 29, wherein a position vertical abovethe axis of rotation is defined as 0° and wherein other positions aredesignated according to their angle in the wheel rotation directionrelative to the 0° position, wherein at least one distance-measuringsensor is provided in a 90° position or in the 270° position at saidfirst radius relative to the axis of rotation of the wheel, wherein atransverse force at the tire is determined by said processing unit froman axial distance measured with said distance-measuring sensor.
 51. Adevice according to claim 50, wherein a further distance-measuringsensor is provided in the 0° position, wherein each one of saiddistance-measuring sensors is combined with one of said first sensors toa common sensing unit, wherein the transverse force at the tire isdetermined by said processing unit from axial distances measured withsaid distance-measuring sensors.